Method of preparing a magnetically stable powder mainly consisting of iron for magnetic recording

ABSTRACT

A METHOD OF PREPARING MAGNETICALLY STABLE IRON POWDER SUITABLE FOR MAGNETIC RECORDING IN WHICH IRON OXIDE HYDRATE, A-FEOI(OH) IS PRECIPITATED FROM A STRONGLY REACTING ALKALINE SOLUTION OF FERROUS HYDROXIDE CONTAINING AT LEAST ONE COMPOUND OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF GERMANIUM, TIN AND ALUMINUM IN SUCH A CONCENTRATION THAT THE ATOMIC RATION OF THE LATTER METAL TO FE IN THE SOLUTION IS A LEAST 0.005 WHILE PASSING AN OXIDIZING GAS THROUGH THE SOLUTION. THE PRECIPITATE IS THEREAFTER SEPARATED FROM THE LIQUID, WASHED, DRIED, AND REDUCED IN HYDROGEN AT 250* TO 500* C.

United States Patent 3,598,568 METHOD OF PREPARING A MAGNETICALLY STABLE POWDER MAINLY CONSISTING OF IRON FOR MAGNETIC RECORDING Cornelis Johannes Klomp and Gerard Willem van Oosterhout, Emmasingel, Eindhoven, Netherlands, assignors to US. Philips Corporation, New York, N.Y. No Drawing. Filed Jan. 29, 1969, Ser. No. 795,078 Claims priority, application Netherlands, Jan. 31, 1968, 6801383 Int. Cl. 1822f 9/00 US. Cl. 75.5AA 1 Claim ABSTRACT OF THE DISCLOSURE A method of preparing magnetically stable iron powder suitable for magnetic recording in which iron oxide hydrate, OL-FCO(OH) is precipitated from a strongly reacting alkaline solution of ferrous hydroxide containing at least one compound of at least one metal selected from the group consisting of germanium, tin and aluminum in such a concentration that the atomic ratio of the latter metal to Fe in the solution is a least 0.005 while passing an oxidizing gas through the solution. The precipitate is thereafter separated from the liquid, washed, dried, and reduced in hydrogen at 250 to 500 C.

The invention relates to a method of preparing a magnetically stable powder mainly consisting of iron, for magnetic recording. A magnetically stablepowder is to be understood to mean herein a powder of which the saturation magnetisation, after it has been exposed to atmospheric air for 24 hours, still is at least 90% of the value measured immediately after preparin the powder. Such magnetically stable powders are obtained by stabilising the freshly prepared powders, namely by immersing them in a suitably chosen organic liquid, for example, dioxane, acetone or ethanol, and then removing them from the liquid and liberating them from the adhering liquid.

iFine iron powders as a material for magnetic recording are known. It has already been proposed to prepare such powders by electrolysis of ferro-salt solutions, while using a mercury cathode. However, the cost involved in the use of said method on a technical scale is considerable. On the other hand it has been found that iron powders prepared by reduction of iron oxides are not very suitable for the use as a material for magnetic recording. It is the object of the invention to improve this.

The conventional method so far of preparing iron powders by reduction of iron oxides consisted in that iron oxide hydrate, a-FeO (OH) was precipitated from an alkaline reacting suspension of ferro-hydroxide in water while introducing an oxidizing gas, after which the precipitate was separated from the liquid, then washed and dried and reduced with hydrogen at a temperature of 250500 C., after which it was finely stabilized. According to the invention the above-mentioned suspension contains at least one compound of at least one metal of the group formed by Ge (germanium), Sn (tin), and Al (aluminum) and that in such a concentration that the atomic ratio r: Me/Fe in this solution is at least 0.005.

It has been found that the method according to the invention enables the preparation of powders which, as regards their usefulness as a material for magnetic record- 3,598,568 Patented Aug. 10, 1971 ing, are considerably better than the known powders which have likewise been obtained by the reduction of iron oxides. This will be illustrated in the following examples. Before describing the examples it is to be noted that for the method according to the invention it is essential that the above-mentioned compound(s) of germanium and/or tin and/or aluminum are already present in the solution of the iron salt during the formation of the precipitate of iron oxide hydrate.

In order to characterize the powders prepared as described in the examples, the properties thereof, which are most important for the usefulness of the material as a material for magnetic recording, have been measured. The results of the measurements are recorded in a table at the end of each of the examples. The magnetic values stated in the table are expressed in Giorgi-units. The symbols used have the following meanings:

,u the magnetic permeability (ratio B/ H) in vacuo,

I the magnetisation coercive force,

H the remanent coercive force,

0 the magnetic moment per kg. in a field of 10 amp./ metre,

a, the remanent magnetic moment per kg. after magnetisation in a field of 10 amp/metre.

EXAMPLE 1 First of all iron powder was prepared in which the formation of the precipitate of a-FeO(0H) took place without the presence in the alkaline liquid of a compound of one of the metals germanium, tin or aluminium. This blank experiment was carried out as follows:

67.2 gms. of FeSO -7H O were dissolved in 336 mls. of distilled water. The resulting solution was poured, while stirring, into a cooled solution of 112 gms. of NaOH in 560 mls. of distilled water. Air at a rate of 5 ls. per min. was then passed through the thus formed suspension of ferro-hydroxide at room temperature and for 166 hours. The a.-FO(OH) precipitated from the mixed solution was washed with distilled water until the wash water had a pH of 6. The precipitate was then rinsed with acetone and dried in air.

Approximately mgms. of the resulting dry iron oxide hydrate were reduced by treating it for 60 min. at a temperature of 350 C. with hydrogen which was supplied at a rate of 940 mls. per min. The resulting iron powder was stabilized. For that purpose it is first immersed in acetone. After some time (for example one hour) the acetone was removed. The powder is then dried in air for a few hours.

In the experiments to be described hereinafter, the mixed solutions in which the percipitates of the iron oxide hydrate were formed, contain germanium oxide, GeO- (a) 33.6 gms. of FeSO -7H O were dissolved in 168 mls. of distilled water. Furthermore 56 gms. of NaOH and 0.0142 gm. of GeO were dissolved in 280 mls. of distilled water, after which the solution is cooled to room temperature. It was then added, while stirring, to the above-mentioned solution of ferrosulphate. Air at a rate of 5 ls. per min. was then passed through the suspension of ferrohydroxide thus formed at room temperature for 24 hours. The formed precipitate was again washed until the wash water had a pH of 6. The iron oxide hydrate was then rinsed three times with acetone and dried in air. A small quantity of the resulting powder is reduced with hydrogen after which it was stabilized as stated in the description ofthe blank experiment. 7 V

The following experiments 1b, 1c and 1d differ from the experiment 1a in that the quantities of dissolved Ge were different. These quantities were successively 0.1279 gms., 0.5 gm. and 1.27 gms., respectively.

The results measured in the various preparations are recorded in the following Table 1.

4 NaOH in 280 mls. of distilled water were prepared, which solutions were cooled to room temperature. One of'the solutions B was added to each of the four solutions A, while stirring. Air at a rate of is. per min. was passed through each of the four thus formed suspensions of ferrohydroxide at room temperature for 24 hours. The four precipitates were washed until the wash water had reached a pH of 6. The washed precipitates were then rinsed three times with acetone and dried in air, after which they were TABLE 1 reduced and stabilized as described in Examples 1 and 2. g fgg g The properties of the resulting metal powders (Experiaccording Me 0 H m H @32 a. ments 3a, 3b, 3c and 3d) are recorded in Table 3.

0 T=-- o n o r experiment Fe (in''seo/mfi) (iiiVsee/mfi) rim/kg.) 1r. TABLE 3 Itblank) 405 650 2. 23 0.31 Powder 1a 0.001 450 702 2. 54 0. 25 prepared 0.010 1, 205 1, 573 2.36 0. 47 according Mo .r.. 10 o. 0. 040 1,304 1, 606 2.22 0 is to r=-- (po-;Ho)X10 0 H. 10 (inVseC. 0.100 experiment F0 (inVsee/mfl) (inVsee/mfl) m./kg.) a.

. bl k .3 The powder obtained accordlng to experiment ldwas 0.002 5%? i 8.20 found to be so pyrophorrc that 1t could not be stabilized. gg 8-833 i i: i 8-2; 2 3d 0.200 1,085 1,539 1.57 0.43

F r t xperim s 10 be described and From the measured results recorded in the above tables the followlng Solutlons Prepared: may be seen that when a quantity of germanium, tin or Four equal Solutions of 335 gms' of FeSOiqHZO in 168 aluminum was in the solution in which the iron oxide hyof distilled Water (solutions drate was precipitated such that in said solution the atomic Four equal solutions of 56 gms. of NaOH in 280 mls. of f i is least the Values of the q distilled water, i.e. a 0.2 N solution, which solutions c and T Wlth respect 9 the were cooled to mommmperature (Solutions obtained in the blank experiment were considerably 1m- Four different solutions of SnCl -2H O in 10 mls. of dis 30 P ed a that to such an extent that the metal powders tilled water (solutions C). The quantities of dissolved Obtained according to lnvemlon Very E y SnCl-2H O in the solutions C are successively 0.0279 a to be used as amaterla for magnetic recordlnggm., 1.0955 gms., 2.73 gms. and 0.273 gm., respectively. Y g IS 3 2 151 t H t b1 d met 0 o prepanngarnagne rca y s a epow er to m g gg gi 2x3 2 23? gfi zg gg z i i 35 consisting mainly of iron, for magnetic recording comformed mixt i O1 ti C ac z d 3. prising the steps of prec prtatrng oc-FO(QH) from a susf 5 lures e S a g a 1r pension of ferro-hydroxrde in water having a concentrag ggz g 6 523223 25 33 igg 3 12 1255222 tion of hydroxyl ions of at least 0.2 normal and containing 24 hours. The resulting precipitates of iron oxide hydrate 40 2 3;? i g g ggg ggggg gf 3 232 25 32; g aq were washed until the pH of the wash water had reached and A1 (aluminum) ingsuch a foncent t T the value 6. The precipitates were then each rinsed three atomic ratio rzMe/Fe in Said solution times with acetone and dried in air. Approximately 150 s t d a mgms. of each of the dry powders were reduced by heatb 3 3 F oilldlzmg sepaiatmg said ing at 350 C. in a stream of hydrogen for 60 min. The a: mm e lqul washmg Mid drymg the pmhydrogen was supplied at a rate of 940 mls. per min The i then reducmg P preclpltate l-lydgogen at a metal powders formed Were stabilized. The following emperature of 25O 500 and then Stablhzmg 51115353052125? survey of the properties of the resulting References Cited TABLE 2 UNITED STATES PATENTS Powder ,717 8/1906 Edison 75 5A p 'gpayed 2,179,810 11/1939 Brill et a1 75 5 according Me i 2,497,268 2/1950 Neel 750 5AA t 0' Ho r v eiipmmas F. 8?. 1.052% 5575.17.33; 5151 2.592.321 4/1952 Neel 75-0.5AA 95 I 3,026,215 3/1962 Fukuda et a1 148 1()5 410 2g: 8-5; 3,206,338 9/1965 Miller et al 148-105 1 310 38} 242 1 3,276,921 10/1966 Freeman 75P-0.5 AA 1 g? 2,660,522 11/1953 Marguaire 75 5AA FOREIGN PATENTS EXAMPLE 3 743,791 3/1954 Great Britain 750.5 Four solutions of 33.6 gms. of FeSO -7H O' in 168 mls. 749265 8/1954 Great Britain 75 O'5 of distilled water were prepared. In each of these solutions was also dissolved a small quantity of Al (SO -16H O DEWAYNE RUTLEDGE Pnmary Exammer and that in the first solution 0.0765 gm. in the second solu- STALLARD: Assistant Examiner tion 3.04 gms., in the third solution 7.60 gms. and in the fourth solution 0.35 gm. (four solutions A). Furthermore four solutions (solutions B) of always 56 gms. of

U.S. C1. X.R. l'48l05 73 9;" UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 598 568 4 Dated Auqust l0 1971 Inventor(s) Cornelis Johannes Klomp and Gerard Willem Van Costerhou It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 28, line should begin as A blank experiment was first carried out, i.e. an iron powder-.

line 31, "aluminium" should be --aluminum-.

lines 47, 49, 65, "is" should be --was-.

Column 3, In Table l, 2 and 3, (LLo'lHoy' should be line 38, "is" should be -was-.

Signed and sealed this 25th day of January 19 72.

(SEAL) fittest:

EDWARD M.FLETGHER,JR. ROBERT GOTTSCHALK Attesting Officer- Commissioner of Patents 

